Railroad car wheels



NO. OF DRAG TESTS Feb. 19, 1963 R BEETLE ETAL 3,078,160

RAILROAD CAR WHEELS Filed May 7, 1959 5o-.-- ll i L 4L L O; A J .9 do l52 Us |.'4 L5 CARBON /o BY WEIGHT iNVENTORS ROBERT H. BEETLE BY HUGO R.LARSON AXI.

Uflitc st e This invention relates to steel railroad car wheels and moreparticularly tosuch Wheels which are manufactured by foundry techniquesand which are characterized by an excellent resistance both to impactand to cracking produced by thermal effects caused by severe serviceconditions resulting from brake malfunctions.

I The railroad car wheels contemplated within the scope of thisinvention are produced by casting a ferrous metal alloy consistingessentially of from about 0.95 percent by weight to less than about 1.30percent carbon, from about 0.40 percent to about 1.00 percent manganese,from about 0.15 percent to about 0.70 percent silicon, up to about0.055'percent sulfur, up to about 0.055 percent phosphorus, and thebalance substantially all iron, it being understood that other elementscustomarily encountered and regarded as impurities in such castings mayalso be present in minor and ineffective amounts. More specifically, thealloys contemplated by this invention should contain from about 0.95percent to about 1.20 percent and preferably about 1.05 percent carbon,from about 0.55 percent to about 0.85 percent, and preferably about 0.70percent manganese, from about 0.20 percent to about 0.50 percent, andpreferably about 0.35 percent silicon, as low a sulfur and phosphoruscontent as is possible, and may contain up to about 0.50 percentchromium and aluminum up to about 0.15 percent, added as a deoxidizer.

According to this invention, railroad car wheels cast to substantiallyfinal form and dimension from such alloys and appropriately heat treateddemonstrate an unexpectedly higher resistance to destructive thermalcracking encountered in previously known similar cast steel wheelshaving compositions characterized principally by a higher carbon contentwhen subjected to severe service condi-' tions resulting from brakemalfunctions or panic or emergency stops.

-It is therefore a principal object of this invention to provide a caststeel railroad car wheel which consists essentially of an alloy withinthe aforesaid composition ranges which is characterized by its abilityto resist the formation of destructive and dangerous cracks in its treadzone when subjected to abnormally severe braking conditions encounteredduring emergency stops or during operation while subjected to aninadvertently constant braking elfort due to a brake malfunction knownin the art as a dragging brake shoe. Other and specifically ditferentobjects of this invention will become apparent from the followingdisclosure, of which the accompanying drawing is a part. In the drawingthe FIGURE is a graphical representation of the relationship of carboncontent in cast steel railroad wheels composed of the alloys of thisinvention and similar previously known alloys, and the ability of suchwheels to resist the formation of cracks in the tread zones undercontrolled braking conditions.

In the manufacture of cast steel railroad car wheels, as previouslyunderstood, certain problems were encountered. Of these, it wasdesirable that such wheels be able to withstand as much tread wear andhave as high a resistance to cracking under impact loading encounteredatent time.

Patented Feb. 19, 1963 satisfactory for normal service, providing theywere heattreated in a particular manner in order to completelyspheroidize the metal carbides present and eliminate a carbide network.

Wheels made in this manner were found to begenerally quitesatisfactory'when subjected to normal usage, however under certainconditions of severe service, otherwise satisfactory wheels were foundto occasionally develop destructive and potentially dangerous cracks inthe tread areas. These cracks were found to have their origin insituations where it was determined that the brakes had malfunctioned byfailing to release completely, causing one or more brake shoes tocontinuously bear on the tread of the wheel while the railroad car waspropelled and may also be caused by repeated emergency stops from highspeeds. dragging brake for obvious reasons. In view of the apparentfunctional causes of these failures, it became apparent that theresulting cracks were engendered by the absorption of abnormally highamounts of energy in the surface of the wheel tread exposed to the brakeshoes and probably were a form of thermal cracking.

In order to substantiate these conclusions a large number of actual caststeel railroad car wheels were tested under reproducible laboratoryconditions which simulated very extreme braking conditions. One of thestandard test procedures used consisted of mounting the wheel to betested on a dynamometer shaft, urging a standard brake shoe against thewheel tread in a braking attitude under a load of 3000 pounds, bringingthe wheel up to a rotational speed equivalent to 45 miles per hour andmaintaining that speed and that braking effort thereon for 30 minutes.During this time about 49,500,000 pounds feet of energy were dissipated.Thereupon the brakes shoe was removed and the wheel air cooled at aspeed equivalent to about 10 miles per hour for 15 minutes and thenfurther cooled while still rotating at about 10 miles per hour by awater spray. The wheel was then inspected for tread cracks, the entirecycle requiring about minutes total This cycle was repeated until thewheel tread exhibited one crack one inch in length, at which time it wasdeemed to have failed and the test was terminated on that particularwheel. Several other similar tests were also performed, but since theresults Were consistent with the results obtained from the describedtests, it is not believed necessary to go into either the details ofthese tests or their specific results.

Prior to this invention, it was not believed that the carbon content ofpreviously known cast steel railroad wheels could successfully bereduced below 1.30 percent carbon utilizing more or less conventionalsand molding techniques and, it was further believed that the carboncontent should be maintained as high as possible within the aforesaidrange of 1.30 to about 1.65 percent by weight, consistent with theability to heat treat the wheel to The former condition is usuallyreferred to as a spheroidize the carbides to break up the carbidenetwork. More specifically, it was believed that utilizing more or lessconventional sand casting methods, that such lower carbon contents wouldso reduce the hardness of the Wheel that excessive wear would result,that casting defects and lack of soundness in the casting would preventsuch lower carbon content wheels from being successfully cast, and thatno significant difference would be achieved in other mechanicalproperties. We have unexpectedly found that contrary to these beliefs,cast steel railway wheels containing from about 0.95 to less than about1.30 percent by weight carbon, from about 0.40 to about 1.00 percentmanganese, from about 0.15 to about 0.70 percent silicon, up to about0.055 percent sulfur, up to about 0.055 percent phosphorus, and whichmay contain minor amounts of other elements such as up to about 0.50percent chromium and up to about 0.15 percent aluminum may be readilymanufactured with no significant difficulty experienced with defects orunsoundness, that the wear rate is not distinguishably greater than thepreviously known higher carbon content wheels and that these wheels havean unexpectedly greater resistance to thermal cracking where exposed tothe abnormally high braking efforts which tend to cause thermal cracksin the prior art wheels.

In order to more particularly point out the invention,

the following representative data is presented. As previously set fortha large number of dynamometer tests as previously described wereperformed on the aforesaid 1.30 to 1.65. percent carbon cast steelwheels. Similarly, a large number of such tests were similarly performedon the wheels of the present invention. Because of the time factorinvolved, if a given test wheel survived as many as 50 cycles of thedrag test performed upon the dynamometer, as previously described, thetest on that wheel was terminated. This arbitrary number of 50 cycleswas selected because of the performance of the higher carbon contentwheels under this test. As would be expected from a test of. this sort,a scatter band of results were observed in the results of the tests onthe prior art 1.30 to 1.65 percentcarbon wheels. In addition, in orderto more clearly point out rather than obscure the invention, arepresentative. number of wheel tests were selected for purposes ofcomparison and illustration. For example, a group of eight wheel testsperformed on such higher carbon .content wheels containing from 1.37 to1.38 percent carbon have been selected in order to show a representativescatter band and to compare these results with similar test results forwheels of this invention. It will be observed from the accompanyingdrawing that all'of the wheels according to this invention survived atleast 50 cycles of the aforesaid test without failure and the teststerminated at that point as signified by the arrows.

More specifically, all the wheels so tested were cast in sand molds fromalloys containing, upon subsequent analysis, the indicated carboncontent as will be set forth. Further, these wheels all contained within0.40 to 1.00 percent manganese, 0.15 to 0.70 percent silicon, not morethan 0.055 percent sulfur, not more than 0.055 percent phosphorus, notmore than 0.50 percent chromium and notmore than 0.15 percent aluminum.After the usual cleaning operations, including the removal of the risersand the like, the wheels were heat treated by heating to a temperatureof between 1650 to 1950 F., preferably about 1800 F. for about one hour,a time sufficient to achieve a stable temperature and to dissolve thecarbides. The wheels were then air cooled and reheated to a temperaturebetween 1400 and 1600 F., preferably about 1500 F. for about. two hours,a time suflicient for stabilization and the hub portions water cooled,the rest of the wheel structures being permitted to air cool. The wheelswere then finish machined and inspected to insure that there were nodefects before testing.

The following tabulated data, is representative of the 4 many testsperformed on such wheels and which has been plotted in the accompanyingdrawing.

1 Test terminated, no crack amounting to 1 in length.

From the foregoing, and from other similar tests, it has been found thatwheels made according to this invention consistently resist thermalcracking, as previously set forth, for at least 50 cycles of the statedtest, while the higher carbon content wheels seldom withstand as many as20 cycles of the test. in terms of total energy absorbed during suchtests, it may be stated that the railroad car wheels made according tothis invention are capable of absorbing at least 2,475,000,000 poundsfeet (corresponding to the energy absorbed in 50 cyclespofsaid test)whereas the prior art wheels seldom are capable of absorbing more thanabout 990,000,000 pounds feet (corresponding to 20 cycles). andfrequently fail at a much smaller value.

From the foregoing, it will therefore be apparent that thepresentinvention provides a solution to a previously unsolvedproblemrelating to relatively high carbon cast steel railroadcar'wheelsa As indicated previously, many slight variationsfrom thespecific examples given. will readily occur tothose skilled in the artand it is tobe understood that .such variations as reasonably fallwithin the scope of the invention are intended to be covered by tnefollowing claims.

What we claim and desire to secure by Letters Patent.

ofthe United States is;

1. An article of manufacture comprising a-cast steel t railroad carwheel characterized by the ability to absorb at least 2,000,000,000pounds feet of energy in the tread zone thereof without forming treadzone cracks more than one inch in length, consisting essentially of fromabout 0.95 to less than 1.30 percent by weight carbon,

from about 0.40 to about 1.00 percent by weight manganese, from about0.15 to about 0.70 percent silicon, not more than 0.055 percent byweight sulfur, not more than 0.055 percent by weight phosphorus, up toabout 0.50 percent by weight chromium, up to about 0.15 percent byweight aluminum and the balance substantially all iron.

2. An article of manufacture-comprising a cast steel railroad car wheelcharacterized by the ability to absorb at least 2,000,000,000 poundsfeet of energy in the tread zone thereof without forming a single treadzone crack more than one inch in length, consisting essentially of fromabout 0.95 to about 1.20 percentby weight carbon,

from about 0.55 to about'0.85 percent by weight manganese, from about0.20 to about 0.50 percent by weight silicon, less than 0.055 percent byweight sulfur, less than 0.055 percent by weight phosphorus, less than0.50 percent by weight chromium, less than. 0.15 percent by weightaluminum, and the balance substantially all iron.

3. Anarticle of manufacture comprising a cast steel railroad car wheelcharacterized by the abilityto absorb at least 2,400,000,000 pounds feetof energy in treadzone thereof without forming a single thermal crack inthe tread zone which is more than one inch in length, consistingessentially of about 1.05 percent by weight carbon, about 0.70 percentby weight manganese, about 0.35

5 percent by weight silicon, less than 0.055 percent by weight sulfur,less than 0.055 percent by weight phosphorus, less than about 0.50percent by weight chronium, less than about 0.15 percent by Weightaluminum, and the balance substantially all iron.

References Cited in the file of this patent UNITED STATES PATENTS786,248 Cowden Mar. 28, 1905 6 Brunner Sept. 13, 1938 Flinn et a1. Aug.17, 1954 FOREIGN PATENTS Belgium Feb. 1, 1951

1. AN ARTICLE OF MANUFACTURE COMPRISING A CAST STEEL RAILROAD CAR WHEELCHARACTERIZED BY THE ABILITY TO ABSORB AT LEAST 2,000,000,000 POUNDSFEET OF ENERGY IN THE TREAD ZONE THEREOF WITHOUT FORMING TREAD ZONECRACKS MORE THAN ONE INCH IN LENGTH, CONSISTING ESSENTIALLY OF FROMABOUT 0.95 TO LESS THAN 1.30 PERCENT BY WEIGHT CARBON, FROM ABOUT 0.40TO ABOUT 1.00 PERCENT BY WEIGHT MANGANESE, FROM ABOUT 0.15 TO ABOUT 0.70PERCENT SILICON, NOT MORE THAN 0.055 PERCENT BY WEIGHT SULFUR, NOT MORETHAN AND 0.055 PERCENT BY WEIGHT PHOSPHORUS, UP TO ABOUT 0.50